Heat exchange apparatus and method



Jan. 3, 1939. o. c. SCHAUBLE HEAT EXCHANGE APPARATUS AND METHOD FiledJune 2, 1936 u b l e B E311? Sm ATTORNEY.

INVENTOR.

Otto C. Scha Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE LummusCompany, New

ration of Delaware York, N. Y., a. corpo- Application June 2, 1936,Serial No. 83,033

11 Claims.

The invention disclosed herein relates to a fluid heater and its furnaceand is especially directed to the construction of a furnace suitable forthe heating of oil in tubes.

My invention refers particularly to an oil heater having its furnacedivided into combustion and convection zones by an internal partition orbridge wall, and with the tubular heating surface formed in coils forforced circulation of oil therethrough. The coils are preferablyarranged so that some are heated by convection from the hot ,gases ofcombustion while other coils may be subjected to direct radiant heatfrom the burning fuel in the combustion chamber.

An object of the invention is to provide a means for effectively coolingthe walls of such a heater which will maintain their temperatures withinsafe working limits and insure continuous operation of the furnace overlong periods.

A further object is to cool the furnace walls by means of air circulatedin passages associated with the walls, and in a manner which isparticularly adaptable to furnaces operating under natural draftconditions.

The invention also includes a new and improved form of furnace having acentral convection flue disposed between two combustion chambers, withan appropriate arrangement of fluid heating tubes disposed in eachchamber and the flue.

In describing my invention I shall refer to the accompanying drawingidentified as follows:

Fig. 1 showing a sectional elevation of a furnace utilizing myinvention, Fig. 2 being a vertical half-section of Fig. 1 taken alongthe line 22 on a vertical plane through the hollow bridge wall.

The drawing shows the double furnace arrangement as defined by a hearthI, a roof 2, end walls 3, and side walls 4. The bottom wall or hearth iselevated above a fioor 5 to form aduct 6 for the flow of cooling air aswill be described more in detail hereinafter. Burners 1 are mounted inthe lower portions of end walls 3. Partition walls or bridge walls 8separate the combustion chamber 9 at each end from the centrallydisposed convection passage I0 through which the hot gases of combustionflow downwardly upon leaving the furnace chamber on their way to thewaste gas flue II and thence to a stack (not shown) Oil heating tubesl2, l3, and M are shown arranged in coils about the combustion chamberfor exposure to radiant heat from the burning fuel andother tubes 15disposed within the convection passage or tube chamber for heating byconvection from the hot gases contacting therewith. The several sets oftubes are shown serially connected, the cool oil entering at 16 andleaving the series at ll. The exact sequence of flow is of no greatimportance for my present purpose but is so described and illustratedmainly for convenience. The arrangement of the coils, however, isimportant in that it provides for effectively heating some of the tubesby radiation in the combustion chamber, without risk of damage to thetubes by direct impingement of the flames. Furthermore, the arrangementof separate combustion chambers as shown, makes it possible to providethe correct proportion of radiantly heated surface to surface heated byconvection, and to obtain a higher overall efficiency than would resultwith all of the radiantly heated surface located in a single largecombustion chamher.

The bridge walls 8 are made hollow to provide spaces for aircirculation, these air spaces being closed at each end by means of thecasing plate 18 which may be regarded as forming a continuation or apart of thefurnace side wall 4. Horizontally disposed baffles l9 and 20provide within the hollow bridgewall serially connected passages 2l, 22and 23 for the flow of cooling air. These passages are of successivelyincreasing flow areas, the air entering the upper passage 21 throughinlet 24 in the end plate [8, passing next through the larger andintermediate passage 22 and finally through the lower and largestpassage 23. The construction is duplicated at the opposite end of thewall, Fig. 2 representing only a section through one half of the settingwidth.

The circulated air leaves the lowermost passage 23 in each bridge wallthrough openings 25 where it joins the stream of spent gases from thefurnace, the gas and air both being drawn into the waste gas flue by thenatural draft afforded by the stack. The air inlet openings 24 arefitted with adjustable dampers 26, and outlet openings 25 withadjustable dampers 2'! for proper regulation of the air flow through thehorizontal coo-ling passages. In the case of the plurality of exitdampers 2'! these may be conveniently controlled for simultaneousoperation, as shown, through a rod 28 and control handle 29.

The flow of air through the hearth cooling passages 5 may also becontrolled by regulating dampers 30 across the inlet openings 3i, theair discharging into the lowermost bridge wall passage 23 and combiningwith the air from that passage for flow through, openings 25 and final 5discharge from the setting with the spent gases.

With the foregoing arrangement of parts it will be seen that by means oithe induced draft afforded by the stack, cool atmospheric air will bedrawn into the several wall cooling passages or ducts and will cause thecooling air to be positively circulated through those passages toprovide eifective cooling of the respective walls. The cooling air isdischarged into the stream of flue gases at a point subsequent to theircontact with the fluid heating tubes and this circulation is maintainedseparate from the flow of heating gases through the furnace.Consequently there is no impairment of combustion conditions within thefurnace and no cooling or dilution of the heating gases prior to theircontact with the fluid heating surfaces. The air absorbs a certainamount of heat in its circulation through the cooling passages butWhatever loss may result is practically negligible in that it iscompensated for by the fact that, for equal values of heat absorption,the total amount of convection surface required with the gases of highertemperature, is less than would be the case with gases that have beendiluted and cooled.

A further benefit derived from the invention lies in the fact that withthe subetmospheric pressures in the wall cooling passages, there is noleakage of cold air into the furnace chamber and consequently no coolingfrom this source of the furnace gases or of heating surfaces that may bein proximity to such wall as in the case of tubes [2 and M which lieadjacent the hearth.

While in the specific embodiment I have referred particularly to adouble form of furnace it will be understood that certain features of.the invention may be applied equally well to other forms of furnacessuch as one having only a single firing chamber, and it is, therefore,my purpose to include these and other variations of construction withinthe scope of the appended claims.

I claim:

1. An oil heater comprising a furnace chamber and a tube chamber, ahollow bridge wall separating said chambers except at their upper ends,a bank of convection heated tubes in said tube chamber, an outlet fiueconnected to said tube chamber below said tube bank, an atmospheric airinlet to the upper end of the space in said bridge wall, and a passageconnecting the lower end of said bridge wall space to said tube chamberbelow said tube bank, said outlet flue affording direct and undivideddischarge of gas and air from said tube chamber to the atmosphere.

2. An oil heater comprising a furnace chamber and a tube chamber at oneend thereof'connected their upper ends, a bank of convection heatedtubes in said tube chamber, an outiet flue connected to said tubechamber below said tube bank, and a cooling passage extending below thefloor of said furnace chamber having an atmospheric air inlet at one endand its opposite end connected to said tube chamber below said tubebank, said outlet flue affording direct and undivided discharge of gasand air from said tube chamber to the atmosphere.

3. In combination, a furnace having walls defining combustion andconvection chambers, fluid-heating tubes exposed to heat of combustionwithin the respective chambers, the tubes of said combustion chamberlying adjacent a wall having an air passage associated therewith. meansconnecting said air passage with said convection chamber for inducing apositive circulation of cooling air through said passage at a pressureless than the pressure within the chamber, and causing said cooling airto be discharged into the stream of hot gases of combustion subsequentto their contact with tubes in the convection chamber.

4. In combination, a furnace having enclosing walls and an interior walldividing said furnace into combustion and convection chambers,fluidheating tubes contiguous to a Wall of each cham ber, air passageassociated with said walls and provided with inlet and outletconnections for inducing positive circulation of cooling air throughsaid passages at pressures less than the pressures within the chambers,said air passages being connected to the atmosphere at their inlet endsand to a region of lower pressure within said convection chamber attheir outlet ends.

5. In combination, a furnace having enclosing walls and an interior walldividing said furnace into combustion and convection chambers,fluidheating tubes contiguous to a wall of each chamber, air passagesassociated with said Walls, means inducing positive circulation ofcooling air through said passages at pressures less than the pressureswithin the chambers, and means connecting said air passages with saidconnection chamber for causing said cooling air to be discharged intothe stream of hot gases of combustion subsequent to their contact withtubes in the convection chamber.

6. A fluid-heating furnace including an internal partition wall dividingthe furnace chamber into combustion and convection zones having acommunicating passage for heating gases therebetWeen, said partitionwall having a hollow interior provided with bafiles to direct the flowof cooling air, said bafiles forming serially connected flow passages ofsuccessively increasing crosssection, means providing for inflow ofcooling air to a passage of relatively small cross-sectional area, andfor outflow from a passage of larger cross-sectional area, meansmaintaining a flow of. heating gases through said zones separate fromthe flow of air through said passages, and means subjecting saidconvection zone and said outflow passage to equal pressure conditions.

'7. A fluid-heating furnace including an internal partition walldividing the furnace chamber into a combustion chamber and a convectionflue having a communicating passage for heating gases therebetween, saidpartition wall having a hollow interior provided with bafiles to directthe flow of cooling air, said bafiies forming serially connected flowpassages of successively increasing crosssection, means providing forinflow of cooling air to a passage of relatively small cros sectionalarea, and for outflow from a passage of larger cross-sectional area intosaid convection flue adjacent its outlet, said last named passage havingcommunication with the outlet of another wall cooiing passage wherebyair from said other passage is combined with said first quantity fordischarge therewith through said outflow means.

8. An oil heater having a furnace comprising oppositely disposedcombustion chambers with top, bottom and end walls, a convection fluebetween the chambers and separated from each by a bridge wall, burnersin the end walls and directed toward the corresponding bridge walls,radiantly heated tubes lying adjacent the top and bottom walls, othertubes disposed within the convection flue, air passages associated witheach bottom wall and bridge wall, and means connecting the outlet endsof said flue and air passages for inducing a flow of cooling air throughsaid passages independent of the flow of heating gases substantiallythroughout their exposure to said tubes.

9. A fluid heater having a furnace comprising oppositely disposedcombustion chambers, a con vection passage located between said chambersand separated therefrom by upright walls each having their upper endsspaced from the furnace roof to provide a passage for heating gases froma combustion chamber to said convection passage, a bank of fluidconducting tubes in said convection passage, air passages within saidupright walls and openings in a side wall of each of said air passagescommunicating directly with said convection passage at a position belowsaid tube bank, and means inducing a flow of gas downwardly through theconvection passage and a flow of. air downwardly through said wallpassages.

10. The method of operating a heat exchanger having fluid heatingsurface and a combustion chamber at each end with an intermediatelydisposed convection flue separated from each combustion chamber by ahollow bridge wall with means for admitting air to the interior thereof,which includes firing the combustion chambers with elements ofcombustion, passing fluid in contact with the heating surface, admittingair to the interiors of said hollow bridge walls, and maintaining astack draft sufiicient to induce a flow of combustion gases through thefurnace in contact with fluid heating surface and to sustain anindependent flow of cooling air through the hollow interior of eachbridge wall entirely out of contact with said heating surface andseparate from said gases except at their discharge from said flue.

11. The method of operating a heat exchanger having fluid heatingsurface and a combustion chamber at each end with an intermediatelydisposed convection flue separated from each combustion chamber by ahollow bridge wall with means for admitting air to the interior thereof,which includes firing the combustion chambers with elements ofcombustion, passing fluid in contact with the heating surface, admittingair to the interiors of said hollow bridge walls, maintaining a stackdraft sufficient to induce a flow of combustion gases through thefurnace in contact with fluid heating surface while sustaining anindependent flow of cooling air through the hollow interior of eachbridge wall entirely out of contact with said heating surface andseparate from said gases except at their discharge from said flue, andregulating the flow of air through the interiors of the hollow bridgeWalls.

OTTO C. SCHAUBLE.

CERTIFICATE OF CORRECTION. Patent No. 2,11 .2,956. January 5, 1959.

OTTO C. SCHAUBLE.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows Page 2,second column, line 12, claim for "passage" read passages; page 5,second column, line 22, claim 11, for "while sustaining" read and tosustain; and

that the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOfficeo Signed and sealed this 7th day of March, A,D 1959.

Henry Van Arsdale.

(Seal) Acting Commissioner of Patents.

